The present invention relates to a linear motor which draws its operating power from ultrasonic vibration above the frequency of 20 kHz which is generated by piezoelectric ceramic. More particularly, the invention relates to a linear piezoelectric ultrasonic motor which linearly operates a slider due to a frictional force generated by applying sinusoidal electric fields with a 90 degree phase difference to a pair of piezoelectric ceramic. This causes an elliptical mechanical vibration on a shaking beam which is connected to two half wave resonators.
For the case of an electrically operated motor such as a solenoid that moves a relatively short distance, its rotating movement should be converted to a linear movement using a gear or a pulley. As a result, when a large force is required, its size and weight becomes too excessive.
Also, an electro magnetically driven motor has a number of disadvantages such as an excessive heat generation and large current requirement. Especially, the motor in a high temperature environment such as near a car engine is prone to malfunction.
A Linear piezoelectric ultrasonic motor has a number of advantages such as the light weight, low power consumption, and possible linear motion without a gear. Also, its speed, and position can be controlled electrically.
Moreover, a forward and reverse motion is possible and there is no slippage during a stop.
The linear piezoelectric ultrasonic motors can be classified based on their operating methods such as a traveling wave type which operates the motor using a traveling wave generated from a flexural wave, and a standing wave type which generates a repeated horizontal and vertical vibration by combining the longitudinal vibration and transversal vibration of an actuator in order to operate the slider.
The standing wave type linear piezoelectric ultrasonic motor basically uses a multiple vibration by combining each actuator that has a different type of operation mode. The standing wave type linear piezoelectric ultrasonic motor comprises an actuator which operates in vertical and horizontal directions and the contacted section transfers a mechanical vibration to the slider.
The longitudinal vibration of a piezoelectric ceramic is transferred to a vibrating part (contact section) which is in contact with the slider and the slider operates due to the friction at the contact part.
Although many different methods are proposed for vibration transfers, no practical method has been realized due to the difficulty in securing a mechanism for the effective operating power transfer to obtain a constant vibration amplitude.